A High‐Efficiency System for Long‐Term Salinity‐Gradient Energy Harvesting and Simultaneous Solar Steam Generation

Abstract The vast energy stored in the ocean, which receives an average solar power of ≈60 000 TW per year, surpasses human energy consumption by three orders of magnitude. Harnessing even a small fraction of it holds great promise in addressing global energy and water crises. Here, an integrated device that achieves unprecedented power density up to 1.1 W m −2 with excellent stability through a salinity concentration gradient induced by solar evaporation, while simultaneously producing clean water at a rate of 1.25 kg m −2 h −1 under one sun irradiation is presented. The remarkable electricity generation capability stems from the unique interlayer structure of polyaniline‐graphene oxide‐MnO 2 (PANI@GO/MnO 2 ) electrodes, enabling the recovery of electrochemical potentials from a wide range of ion salinity concentrations within the device and the additional Donnan potential generated by the anion‐exchange membrane. Furthermore, periodic flipping of the device effectively reactivates the electrodes and suppresses salt accumulation, enabling long‐term operation. Notably, a prototype device of 8 × 25 cm 2 exhibits a short‐circuit current of 10 mA and an open‐circuit voltage of 10.2 V, as well as a clean water production rate of 24.8 g per hour. These findings shed light on the reliable technology for power and freshwater supply in marine environments.